Silvicultural considerations are playing an increasingly determinant role in the development of new forest harvesting techniques and machinery. This is particularly so in relation to the slow growing trees of the Boreal Forest type regions of the world.
The harvesting method most widely used in the Canadian Boreal Forest employs tracked feller-bunchers to prepare bunches of full trees; wheeled skidders equipped with wire or grapple means to gather the bunches of full trees and move them to truck roads, and delimbers located at the truck roads to remove the limbs and tops, and to pile the stems for subsequent truck transportation.
This method and apparatus for carrying out the same cause silvicultural damage in at least three ways namely (1) nutrient, seed sources, and plant shelter are removed from the cut-over area, (2) the broom configuration of the skidder's full tree loads sweeps down young growth in its path and (3) a blanket of tops and branches covers large areas of productive land along the truck roads and prevents regrowth there for many years. Added to the silvicultural damage is the direct economic damage of the cost of disposing of the road-side branch and top piles. To avoid some of these damages requires a change from the above described method to one which leaves branches and tops at the same location where the trees had grown.
The original manual methods of tree harvesting achieve the desired silvicultural ends, but economics preclude their use. Many different types of apparatus have been developed, some of which might meet the desired end result. Some of these are represented by the teachings in Maradyn's U.S. Pat. No. 3,498,350, Eynon's Canadian Patent 835,144, Larson's U.S. Pat. No. 3,468,352 and Siiro's U.S. Pat. No. 3,461,928. All of the units disclosed therein combine felling, delimbing and topping functions. Some include one or more of cross-cutting, loading and transportation functions. None have achieved wide commercial success because of unattractive economics stemming from machine complexity and the productive limitation of a one-tree-at-a-time process.
In recent years processing heads have been introduced into the tree harvesting field. These are exemplified by the type disclosed in Hamilton's Canadian Patent 1,034,021 and those known commercially as the Steyr K.P. 40 from Austria and the F.M.G. 762 from Finland. Some, like the F.M.G. 762, are designed to fell and process the trees into discrete lengths. Others, like the K.P. 40, process prefelled trees into discrete lengths. Such devices have achieved significant commercial success in Europe and are now being introduced into North America. When they are employed at the growing site of the trees that is where the branches and tops will be left. These devices will therefore contribute to a significant reduction in silvicultural damage. What remains to be determined is the optimum method for their employment and thereby the optimum number of functions they should incorporate.